The present invention concerns combinations of two or more active ingredients for inhibiting or controlling nitrification of ammonia in arable topsoil and subsoil.
Reduced nitrogen, such as that contained in ammonia, ammonium compounds, or nitramide, present in arable soil is rapidly transformed into nitrates via intermediate nitrite stages by bacterial action. The rates at which nitrification proceeds are largely determined by the temperatures, moisture contents, pH, and bacterial activities of the soils involved. A counteracting effect here is that, unlike the nitrogen of ammonia or ammonium compounds, that of nitrates will not be sorbed by the sorbing agents present in arable soil, and will thus either precipitate out and be washed away by surface runoff, or will end up being deposited in deep-lying strata extending down to the water table and below levels accessible to plants. Under adverse weather or soil conditions, runoff losses may exceed 20% of total available reduced nitrogen. To be added to these losses are denitrification losses due to reduction of nitrates formed by nitrification processes to gaseous compounds under anaerobic conditions, losses that may reach comparable levels.
Employing suitable chemicals to inhibit or control nitrification can promote utilization of nitrogen fertilizers by plants. Moreover, this approach provides further benefits in that it reduces nitrate concentrations in ground water and surface runoff, and counteracts nitrate enrichment in cultivated plants, particularly forage crops.
In addition to substituted pyrazoles (U.S. Pat. No. 3,494,757, DD 133088), other known solutions to these problems involve employing dicyanodiamide (DCD) (DE 2702284, DE 2714601), guanyl thiocarbamide (JP 7301138), thiocarbamide (DE 2051935), 1,2,4-triazole, 4-amino-1,2,4-triazole (JP 7104135), or other triazole derivatives (U.S. Pat. No. 3,697,244, U.S. Pat. No 3,701,645).
Combinations of active ingredients supposedly superior to the above-mentioned compounds when employed alone have also been recommended. Among those combinations worth noting here are admixtures of pyrazoles and DCD (DD 222471) or guanyl thiocarbamide (DD 247894), admixtures of 4-amino-1,2,4-triazole (ATC) and DCD (SU 1137096), and amalgams of, e.g., ATC in carbamide/thiocarbamide or carbamide/DCD-mixtures (DD 227957). Employing admixtures of dicyanodiamide and ammonium thiosulfate has also been recommended (DE 3714729).
The disadvantages of these known nitrification inhibitors are their low efficacies, which implies that large dosages will be required, volatilities or instabilities that are too high to allow them to be of much benefit in practical applications, or decomposition rates that are too rapid for the types of applications involved. Moreover, although some of these inhibitors retard nitrification to acceptable degrees, their efficacies are severely reduced by "incompatibility reactions" with several types of fertilizers.